The present invention relates to retractable outside rear view vehicle mirrors of, and more specifically, to vehicle door mirrors which are swingable by electrical means between an extended position and a folded position.
Japanese Patent Provisional (KOKAI) Publication No. 62-94444 shows a conventional retractable door mirror assembly. This door mirror assembly, as shown in FIG. 7, includes a mirror base 104, a swing shaft 105 fixed to the mirror base 104, a mirror housing 111 rotatably mounted on the swing shaft 105, and an ultrasonic motor (surface wave motor) 112 which is coaxial with the swing shaft 105 and which is arranged to directly rotate the mirror housing 111.
In general, a retractable mirror must have a predetermined holding torque (80 Kgfcm, for example) to withstand external forces (due to wind and collision against obstacles). In the above-mentioned conventional example, therefore, it is necessary to increase the radii of the rotor and stator of the ultrasonic motor, to increase the force of a spring for pressing the rotor on the stator, and to increase the friction between the rotor and stator. However, the large rotor and stator increases the total size of the mechanism. The strong spring tends to decrease the facility of movement of the rotor, entail additional power consumption to rotate the mirror against the strong spring force by applying a higher voltage to the piezoelectric element, and decrease the durability of the piezoelectric element. The greater frictional force between the stator and rotor decreases the durability of the mechanism.